Abstract. Carbon (C) and nitrogen (N) released from biomass burning have multiple
effects on the Earth's biogeochemical cycle, climate change, and ecosystem.
These effects depend on the relative abundances of C and N species emitted,
which vary with fuel type and combustion conditions. This study
systematically investigates the emission characteristics of biomass burning
under different fuel moisture contents, through controlled burning experiments with
biomass and soil samples collected from a typical alpine forest in North America.
Fuel moisture in general lowers combustion efficiency, shortens flaming phase, and
introduces prolonged smoldering before ignition. It increases emission factors of
incompletely oxidized C and N species, such as carbon monoxide (CO) and ammonia
(NH3). Substantial particulate carbon and nitrogen (up to 4 times C in CO
and 75% of N in NH3) were also generated from high-moisture fuels, maily
associated with the pre-flame smoldering. This smoldering process emits particles that are
larger and contain lower elemental carbon fractions than soot agglomerates commonly
observed in flaming smoke. Hydrogen (H)/C ratio and optical properties of particulate matter
from the high-moisture fuels show their resemblance to plant cellulous and
brown carbon, respectively. These findings have implications for modeling
biomass burning emissions and impacts.